JAJSF36L November 2008 – February 2019 ADC14155QML-SP
PRODUCTION DATA.
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The ADC14155QML-SP is designed to operate with an internal 1-V reference, or an external 1-V reference, but performs well with external reference voltages in the range of 0.9 V to 1.1 V. The internal 1-V reference is the default condition when no external reference input is applied to the VREF pin. If a voltage in the range of 0.9 V to 1.1 V is applied to the VREF pin, then that voltage is used for the reference. The VREF pin should always be bypassed to ground with a 0.1-µF capacitor close to the reference input pin. Lower reference voltages will decrease the signal-to-noise ratio (SNR) of the ADC14155. Increasing the reference voltage (and the input signal swing) beyond 1.1-V may degrade THD for a full-scale input, especially at higher input frequencies.
It is important that all grounds associated with the reference voltage and the analog input signal make connection to the ground plane at a single, quiet point to minimize the effects of noise currents in the ground path.
The Reference Bypass Pins (VRP, VRM, and VRN) are made available for bypass purposes. Each of these pins should be bypassed to ground with a 0.1-µF capacitor. A 0.1-µF and a 10-µF capacitor should be placed between the VRP and VRN pins, as shown in Figure 24. This configuration is necessary to avoid reference oscillation, which could result in reduced SFDR and/or SNR. VRM may be loaded to 1 mA for use as a temperature stable 1.5-V reference. The VRP and VRN pins should not be loaded.
Smaller capacitor values than those specified will allow faster recovery from the power down mode, but may result in degraded noise performance. Loading any of these pins, other than VRM, may result in performance degradation.
The nominal voltages for the reference bypass pins are as follows:
VRM = 1.5 V
VRP = VRM + VREF / 2
VRN = VRM – VREF / 2